Hi, Diana!
I'm so glad you reached out to the Disney Parks Moms Panel!
There are two Quick Service restaurants that come to mind for me because I've watched the fireworks nearby these spots in the past. First, the best view (in my opinion) from a Quick Service restaurant is in Epcot's Mexico.
La Cantina de San Angel has seats right along the water and can be a fun spot to watch the show. I will warn you that it can get crowded and may be tricky to snag a table.
The other spot that comes to mind is in Epcot's England. The
Yorkshire County Fish Shop has tables along the water. I would say the angle of the restaurant will not be the clearest view of the show but could be worth the try if you really want to sit at a table and eat. Once again, I'll say it might be tricky to find a seat!
Table or no table, you're going to love the Illuminations show! My family always makes sure we watch it at least once during a visit to Walt Disney World Resort!
-Jen